DE60312677T2 - FUEL CELLS OXYGEN REMOVAL AND PREPARATION SYSTEM - Google Patents

Abstract

A fuel cell having an anode, a cathode and an ion exchange membrane is supplied by hydrogen fuel through an anode fuel delivery conduit. A recirculation loop is provided to recycle gases in the fuel delivery conduit to a mixing point where a controlled flow rate of fuel is supplied and mixed therewith. Any oxidant species remaining in the fuel delivery conduit are thereby combusted in a controlled manner to avoid damage to the fuel cell membrane-electrode assembly. Small quantities of oxidant may be deliberately introduced into the fuel delivery conduit to generate water vapor and heat to pre-condition the fuel delivered to the anode. Such preconditioning assists in hydration control of the membrane, and temperature control of the membrane-electrode assembly for optimum fuel cell performance.

Description

The The present invention relates to fuel cells, and more particularly to methods and apparatus for the controlled removal of oxidants from a fuel cell fuel supply stream.

Conventional electrochemical fuel cells convert fuels and oxidants into electrical energy and a reaction product. A typical design of a conventional fuel cell 10 is in 1 shown showing the various layers in an exploded view for clarity. A solid polymer ion exchange membrane 11 is between an anode 12 and a cathode 13 arranged. The polymer membrane allows protons to pass across the membrane but blocks the passage of electrons. Typically, the anode 12 and the cathode 13 both formed of an electrically conductive, porous material, such as porous carbon, to which are bound small particles of platinum and / or other noble metal catalysts. The anode 12 and the cathode 13 are often directly adjacent to the respective adjacent surface of the membrane 11 tethered. This combination is commonly referred to as membrane electrode assembly or MEA.

Externally on the polymer membrane and the porous electrode layers are an anode fluid flow field plate 14 and a cathode fluid flow plate 15 arranged. The fluid flow field plates 14 . 15 are formed of an electrically conductive, non-porous material through which the respective anode electrode 12 or cathode electrode 13 can be contacted electrically. At the same time, the fluid flow field plates must be capable of allowing the supply and / or removal of fluid fuel, oxidant and / or reaction products (and / or other diluent gases that do not participate in the reaction) to or from the porous electrodes. This is accomplished conventionally by forming fluid flow passages in a surface of the fluid flow field plates, such as grooves or channels 16 in the surface facing the porous electrodes.

2 shows a plan view of a typical fluid flow channel 16 as a serpentine structure 20 in one side of the anode 14 (or cathode) is arranged and an inlet port 21 and an outlet port 22 having. Many different configurations of the fluid flow channel can be used.

In a typical application, the anode fluid flow field plate becomes 14 Hydrogen gas through the inlet port 21 in the serpentine canal 20 admitted. At the cathode fluid flow plate 15 becomes oxidant (eg, oxygen gas) from the inlet port into the serpentine channel 20 admitted.

Before starting up a fuel cell 10 After the first assembly, initial assembly, repair, longer periods of inactivity or standby, accumulation of air may occur in the fuel flow channels and the fuel supply lines, ie, generally within the fuel supply path of the fuel cell. There is therefore a need to remove this air, more specifically, to remove the oxygen in the air from the anode fuel supply path before any oxygen fuel or oxygen-rich gas mixture of the anode 12 and the membrane 11 is supplied.

This removal of oxygen prior to delivery of fuel is important to prevent unwanted uncontrolled catalytic combustion occurring at the surface of the anode 14 occurs and in local heating, dehydration and possible puncture of the proton exchange membrane 11 results.

In the prior art, it is common practice to use the anode channels 16 and purging other parts of the fuel supply lines by passing an inert gas, such as nitrogen, for a period of time prior to the introduction of hydrogen fuel.

This Process requires a local supply of nitrogen, the general contained in a printing cylinder, and their periodic replacement. It is desirable to eliminate this requirement and thereby the operating and maintenance needs of the Simplify system. This is especially important if the Fuel cell is already installed in the field, z. B. as part a propulsion system of a vehicle, where the accessibility of a purge gas and indeed the accessibility the fuel cell limited may be.

WO 01/39310 discloses an operating system for a direct cryoprotectant-cooled fuel cell power plant for generating electrical energy by reducing and processing oxidant fluid / reactant streams. The system comprises a proton exchange membrane fuel cell powered by hydrogen supplied by a reformer and a burner for processing hydrocarbon fuel. An anode exhaust passage receives an anode exhaust stream exiting the fuel cell, which then passes through a heat exchanger connected to the exit of the reformer. a burner is supplied.

The JP 1 124 962 discloses an alkaline electrolyte fuel cell system in which a fuel cell is preheated by combusting hydrogen and oxygen in a catalytic burner connected to a hydrogen circulation circuit, purging nitrogen gas into the fuel cell, and replacing with reaction gas.

The JP 5089899 discloses an internal reforming type fuel cell fuel cell in which at least a portion of the fuel is combusted by a catalytic combustor that provides combustion gas to both the anode and cathode sides of the fuel cell.

The WO 01/97310 discloses a catalytic humidifier and heater for one Hydrogen fuel cell using a proton exchange membrane. Air and hydrogen are fed to a catalytic reactor, whereby heated moistened Air is generated, which then flows through the fuel cell stack.

It It is an object of the present invention to provide a convenient method and a device for removing oxygen from the fuel supply lines to provide an electrochemical fuel cell.

It Another object of the present invention is a device through which the removal of oxygen from the Fuel supply lines of an electrochemical fuel cell can be automatically effected.

One Another problem associated with the startup of fuel cells is, is that the membrane electrode assembly generally only with Optimum efficiency works after having an ideal operating temperature and an ideal level Humidification of the membrane has reached. Conventionally, such becomes optimum efficiency only after a period of operation of the Fuel cell reached.

It is another object of the invention to provide a device by preconditioning a fuel and / or oxidant gas stream, to speed up the humidification of the membrane-electrode assembly and / or warming up the membrane-electrode assembly to accelerate to an optimal operating state.

In one aspect, the present invention provides a fuel cell system comprising:
a fuel cell having an anode, a cathode, and an ion exchange membrane disposed therebetween;
a fuel supply line, which
a fluid flow field plate forming part of the anode and having a fluid flow passage extending therethrough;
a fuel supply inlet connected to one end of the fluid flow passage;
a fuel supply outlet connected to another end of the fluid flow passage; and
a fluid flow regulator for controllably varying the amount of fuel supplied to a mixing point in the fuel supply tube;
wherein the fuel cell system further comprises a recirculation line extending between the fuel supply outlet and mixing point, the mixing point comprising either (i) a reaction chamber for reacting fuel or (ii) a premixing chamber for mixing fuel from the fluid flow regulator with oxidizer species from the recycle line.

In another aspect, the present invention provides a method of operating a fuel cell having an anode, a cathode, and an ion exchange membrane disposed therebetween, comprising the steps of:
Supplying fuel from a fuel source to an active surface area of the anode via a fuel supply line;
Returning fluid within the fluid delivery conduit to a mixing point upstream of the active surface area of the anode;
Effecting controlled combustion of fuel and oxidant species within the fuel feed line at the mixing point in a reaction chamber.

embodiments of the new invention will now be given by way of example and with reference on the attached Drawings in which:

1 is a cross-sectional explosion drawing of a fuel cell according to the prior art;

2 a plan view of a fluid flow field plate in the fuel cell according to 1 is;

3 Fig. 12 is a schematic diagram of a first arrangement of an oxygen removal system according to the present invention;

4 Fig. 12 is a schematic diagram of a second arrangement of an oxygen removal system according to the present invention;

5 a schematic diagram of a preconditioning system for controlled burning tion of fuel and oxidizer in a fuel supply line according to the present invention; and

6 FIG. 12 is a schematic diagram of another preconditioning system for controlled burning of fuel and oxidant in a fuel supply line according to the present invention. FIG.

One Method, oxygen removal from the fuel supply path It is to achieve the oxygen in a controlled catalytic combustion of hydrogen outside to use the fuel cell.

With reference to 3 is a fuel cell 10 on fuel supply lines 30 . 31 and oxidizer / exhaust pipes 32 . 33 connected. The fuel supply lines 30 respectively. 31 make an inlet 30 and an outlet 31 for supplying to and removing from the anode fluid flow field plate 14 ( 1 ) while the oxidant supply line 32 a supply of the oxidant to an inlet end of the cathode fluid flow field plate 15 provides and the exhaust pipe 33 provides an outlet for removing unused oxidant and reaction products from the cathode.

A fuel supply (eg, hydrogen) is connected to a system inlet 34 connected to a reaction chamber 35 leads. A return loop 36 extends between the outlet 31 and the reaction chamber. The return chamber 36 includes a pump 37 and can be done using a two-way valve 38 be turned on.

The reaction chamber 35 contains a suitable catalytic material distributed on a support to facilitate removal of passing oxidants according to techniques well known in the art. Presently preferred catalytic materials include precious metals such as platinum or aluminum alloys dispersed on a ceramic support such as alumina.

In a normal operating mode, the fuel cell becomes a hydrogen fuel via the system inlet 34 , preferably via a flow regulator or a metering valve 39 provided. The hydrogen fuel enters the inlet port 21 and the anode fluid flow field plate 14 ( 1 ), where it is at least partially consumed. Any unused fuel or inert dilution fluid from the fuel supply may be via a fuel system outlet 22 be blown out when the two-way valve 38 is connected in a blow-out.

If it is determined that the anode (fuel) stream is contaminated, or if it is suspected to be contaminated by oxidant fluid, the system is switched to a recycle mode of operation. In this configuration, the two-way valve 38 switched so that the fuel cell outlet 31 to the return loop 36 connected. If it is necessary to maintain the fluid circulation, the return pump becomes 37 switched on. In this way, the anode fluid stream is recycled, passing through the reaction chamber 35 occurs where the oxidant species are removed from the fluid stream, preferably by reaction with a controlled supply of hydrogen gas from the fuel system inlet 34 and the flow regulator 39 ,

In this way, the combustion of hydrogen and oxidant species only in the reaction chamber 35 and not in the fuel cell 10 causes.

The return operation mode may be started according to any desired prevailing condition. These conditions may include any one or more of the following: (i) automatic detection of oxidant in the fuel supply line inlet 30 and / or outlet 31 by means of a suitable sensor mechanism (described later); (ii) automatically detecting a period of non-use of the fuel cell that exceeds a predetermined elapsed time limit; (iii) automatically detecting a period of use of the fuel cell that exceeds a predetermined elapsed time limit; (iv) automatic detection of a service condition, ie after detection of a fuel cell maintenance condition; and (v) manual initiation by a user.

During the recirculation mode, the gases in the fuel cell can pass through the return loop 36 and through the reaction chamber 35 into which hydrogen gas is introduced in a controlled manner, are recirculated until all unwanted oxygen is eliminated. This recycle mode may automatically stop for a predetermined period of time, or it may be automatically resumed until a reduction of undesirable species of oxidant below a predetermined threshold is detected. Alternatively, the duration of the return mode may be manually controlled by the user.

The metered supply of hydrogen fuel from the flow regulator 39 Ensures that the combustion of the fuel and the oxidant on the volume of Reaktionskam mer 35 is limited, and that no combustion takes place within the fuel cell itself.

The presence of an oxidant species in the fuel supply lines and in the anode lines can be detected by a number of methods. A low voltage across the no-load fuel cell stack 10 near zero is often a good indicator of the presence of oxygen on the anode electrode side. After this oxygen has been substantially removed, the hydrogen will pass through the reaction bed and onto the fuel cell anode surface, thereby increasing the stress-free stress and indicating successful oxygen elimination.

So In a presently preferred embodiment, prior to operation the fuel cell tested the voltage without load. If those Voltage without load is lower than a predetermined limit, The system determines that before entering a normal operating mode a return mode of operation using a low current of hydrogen supply should be started. In another embodiment, the voltage without load during of the return mode continuously monitored, until the voltage without load exceeds a predetermined limit.

In a further embodiment can monitor the oxygen level by monitoring the temperature of the reaction chamber or an outlet thereof monitored using a suitable thermocouple or temperature dependent resistor become. While the period in which oxygen enters with fuel in the reaction chamber is reacted, the temperature of the reaction chamber or the Gas stream emerging from the reaction chamber, rise. If this temperature rise ends, the temperature begins to fall or the temperature rise drops below a predetermined rate of increase, can be found that the oxygen level below a appropriate limit has been reduced, indicating that the fuel cell is brought into a normal operating mode can.

After this the oxygen has been removed, can the hydrogen flow rates increased to such levels be with the normal power supply through the fuel cell are consistent and normal operation can begin.

Referring to 4 For example, an alternative method of achieving oxygen removal from the fuel supply path is to use the oxygen in a controlled combustion of hydrogen within the fuel cell.

In this embodiment, the reaction chamber 35 removed and the return loop 36 returns the recirculated gas stream to a mixing point 40 where he uses the controlled low flow of hydrogen fuel from the fuel system inlet 34 and the flow regulator 39 is mixed.

Preferably, the mixing point 40 a premixing chamber 41 comprising a plurality of mixing sheets or other suitable physical structure to effect intimate mixing of the fuel fluid with the recycled fluid prior to entry into the fuel cell. In this way, a very controlled low level reaction is effected at the anode of the fuel cell in such a manner as to prevent any significant level of damage to the fuel cell.

This is based on the catalytic activity of the anode surface in the fuel cell 10 to promote the reaction of fuel and oxidant in situ. Provided that a controlled dosing of the hydrogen and a good premix takes place before entering the fuel cell, local heating effects are avoided within the anode and there is a good reaction distribution, which avoids damage to the fuel cell.

Of the Measured hydrogen fuel can be a hydrogen-rich gas have, for. A mixture of hydrogen and inert diluent fluid, what further improvement in the fuel and oxidant mixture offers.

Similar to the embodiment of 3 Automatic control means may be provided to determine when the return mode must be started and for how long before it can be switched to a normal operating mode.

One Another aspect of preventing or limiting damage to the Membrane electrode assembly is to ensure that the fuel of the anode with a optimal temperature and / or humidity is provided. During one Start-up phase can be the control of temperature and / or humidity Fuel also the process of obtaining an optimal operating condition accelerate in the fuel cell.

Referring now to 5 can be an adaptation of in conjunction with 3 be described in order to precondition the fuel flow by introducing water or steam to the moisture in improve or maintain the fuel gas flow. Another advantage of this arrangement is that the temperature of the fuel flow can also be controlled.

In order to achieve this fuel preconditioning, provision is made for introducing oxidant (eg air) into the reaction chamber 35 to arbitrarily increase the reaction of hydrogen with oxygen for the purpose of generating water and heat.

An oxidant supply line 50 is connected to a source of suitable oxidizing agent. In the preferred embodiment shown, this source is conveniently the same source of oxidant used to supply the cathode, namely the oxidant supply line 32 , The oxidant supply line 50 it's about a valve 51 connected, which may also include a flow regulator (not shown separately). This system configuration can be with or without the return line 36 that in the 3 and 4 is shown used.

The provision of controlled amounts of oxidant to the reaction chamber 34 results in a predetermined reaction rate of hydrogen and oxygen in the reaction chamber, thereby allowing the control of the temperature and humidity of the fuel gas, that of the fuel cell 10 via a fuel supply line inlet 30 is supplied (of course, assumed that the fuel supply from the flow regulator 39 over what is needed by the oxidant supply, provides excess fuel.

The flow of water or water vapor to the fuel cell 10 (and its continued repatriation when combined with the return loop 36 by using a preconditioned fuel stream, it is possible to control the humidification state of the membrane and thus maintain conductivity.

These possibility is particularly in the operation of fuel cells from the open cathode design useful, which tend to membrane dehydration if they are not for extended periods operate.

Energy is generated during the reaction in the reaction chamber 35 thus providing the opportunity to supply heat directly to the fuel cell or any other part of the associated system by means of a heat exchanger / transfer mechanism. This may be particularly useful when a fuel cell is cold-started, where the rapid increase in temperature will ensure a shorter time to normal operating temperature and maximum performance. In any case, the use of a catalytic reactor upstream of a fuel gas inlet and / or in a recycle loop provides the additional flexibility of controlling the fuel gas moisture and introducing heat across the gas stream.

Referring to 6 Another arrangement is shown which includes both providing, humidifying and preheating the fuel flow to the anode of the fuel cell 10 as well as the separate humidification and preheating of the oxidant stream to the cathode of the fuel cell 10 allowed.

In this arrangement, the fuel system inlet 34 so closed that he has a first reaction chamber 35 within the fuel supply line 30 supplied via an oxidant supply line 50 is supplied. The oxidant supply line 32 includes a second reaction chamber 60 passing through a fuel supply line 61 is supplied. Suitable valves 62 . 63 control the flow of oxidant and fuel to the respective first and second reaction chambers 35 . 60 These valves may also include flow controllers for varying the flow rate according to a desired level of humidification and / or preheating.

It will be understood that each or both of the first and second reaction chambers may be used independently of the other. In addition, the system could according to 6 can also be used in conjunction with a return loop, as used in conjunction with 3 is described.

The preconditioning mode used in conjunction with 5 and 6 can be started according to any desired prevailing state. These conditions may include one or more of the following: (i) automatically detecting that a period of non-use of the fuel cell exceeds a predetermined elapsed time limit; (ii) automatically detecting that a period of use of the fuel cell exceeds a predetermined elapsed time limit; (iii) automatic detection of a service condition, ie after detection of a fuel cell maintenance condition; (iv) automatic detection of a predetermined temperature or humidity condition in the fuel supply line or fuel cell, and (v) manual initiation by a user.

The preconditioning mode of operation may automatically continue for a predetermined period of time, indefinitely or automatically until a suitable temperature or humidity condition is detected in the fuel supply line or the fuel cell. Alternatively, the duration of the preconditioning mode may be manually controlled by the user.

For the sake of convenience, within the present description, the fuel cell has become 10 is described as having only a single anode, membrane and cathode. It will be understood, however, that according to conventional fuel cell construction, more membrane-electrode assemblies are used in series or in parallel in a stack to increase the voltage and / or power supply. Accordingly, the fuel supply line typically includes a plurality of anode fluid flow field plates, and the oxidizer supply line typically includes a plurality of cathode fluid flow field plates. The principles of the present invention apply equally to such membrane electrode assembly stacks.

The Invention is relative a conventional MEA containing a polymer membrane having. But she is also for other types of fuel cells relevant.

Other embodiments move in the attached Claims.

Claims (25)

Fuel cell system with: a fuel cell, an anode, a cathode, and an ion exchange membrane disposed therebetween having; a fuel supply line, which a Fluid flow field plate, forming a part of the anode and a fluid flow channel, having extending therethrough; a fuel supply inlet, at one end of the fluid flow channel connected; a fuel supply outlet connected to a other end of the fluid flow channel connected; and a fluid flow regulator for controlled Varying the amount of fuel that reaches a mixing point in the fuel supply inlet supplied is, comprises, wherein the fuel cell system further comprises a return line includes, extending between the fuel supply outlet and mixing point extends, wherein the mixing point either (i) a reaction chamber for reacting fuel or (ii) a premixing chamber for mixing fuel from the fluid flow regulator with oxidant species from the return line includes. A fuel cell according to claim 1, wherein the reaction chamber a catalyst material. Fuel cell according to one of the preceding claims, wherein the return line Switchable with the fuel supply outlet by means of a two-way valve connected is. Fuel cell according to one of the preceding claims, which further comprises detection means for detecting a level, on the oxidant species in at least a portion of the fuel supply line available. Fuel cell according to claim 4, wherein the detection means Means for testing an open circuit voltage across the anode and the cathode having the fuel cell. A fuel cell according to claim 1, further comprising control means for switching the fuel cell between a normal operating mode, in that a relatively high flow rate is supplied to fuel of the anode and to the oxidizing agent of the cathode, and a return mode in which a relatively low flow rate of fuel is present with oxidant that over the return line supplied is supplied to the anode becomes. A fuel cell according to claim 1, further comprising control means for switching the fuel cell between a normal operating mode, in that a relatively high flow rate is supplied to fuel of the anode and to the oxidizing agent of the cathode, and a return mode in which a relatively low flow rate of fuel is present with oxidant that over the return line supplied is supplied to the fuel supply line. A fuel cell according to claim 1, which further comprises a Oxidant supply line extending from a Oxidant supply to the mixing point in the fuel supply inlet extends. A fuel cell according to claim 8, further comprising a Oxidant flow regulator for controllably varying the amount of oxidizing agent, fed to the mixing point becomes. A fuel cell according to claim 9, wherein the oxidant flow regulator having a valve that contains the oxidant supply line connects to a cathode oxidant supply line. The fuel cell of claim 8, wherein the mixing point comprises a reaction chamber for reacting fuel from the fluid flow regulator Having oxidant species from the oxidant supply line. A fuel cell according to claim 11, wherein the reaction chamber a catalyst material. A fuel cell according to claim 1, which further comprises means for effecting a controlled combustion of fuel and Oxidant species within a cathode flow supply line includes. The fuel cell of claim 13, wherein the cathode flow supply line a fluid flow field plate, which forms part of the cathode and one through it extending fluid flow channel having; an oxidant supply inlet connected to one end of the Cathode fluid flow channel connected; and an exhaust outlet which is at another end the cathode fluid flow channel is connected has. A fuel cell according to claim 14, wherein the means for effecting controlled combustion within a cathode have a fuel supply line extending from a Fuel supply to a mixing point in the oxidant supply line extends. A fuel cell according to claim 15, wherein the mixing point in the oxidant supply line, a reaction chamber for reacting fuel from the fuel supply line with oxidizer species from the oxidant supply. The fuel cell system of claim 1, further Control means for controlled variation of the flow rate of the fuel and / or the oxidizing agent in order to predetermined level To achieve humidification of the fuel flow, which is supplied to the anode. The fuel cell system of claim 1, further Control means for controllably varying the flow rate of the fuel and / or the oxidizing agent to a predetermined Measure preheating reach the fuel flow, which is supplied to the anode. Method for operating a fuel cell with an anode, a cathode, and an ion exchange membrane interposed therebetween, which has the steps: Feeding fuel from one Fuel source to an active surface area of the anode by means of a fuel supply line; Returning from Fluid within the fluid supply line to a mixing point upstream of the active surface area the anode; Effecting a controlled combustion of fuel and oxidant species within the fuel supply line at the mixing point in a reaction chamber. The method of claim 19, further comprising the step Controlled variation of the amount of fuel includes supplied to the mixing point becomes. The method of claim 19 or 20, further the step of detecting a level on the oxidant species present in at least part of the fuel supply line has. The method of claim 19, further comprising the steps switching the fuel cell between a normal operating mode, in that a relatively high flow rate is supplied to fuel of the anode and to the oxidizing agent of the cathode, and a return mode in which a relatively low flow rate of fuel is present with oxidant supplied in the recycle fluid, supplied to the anode becomes. The method of claim 19, further comprising the steps switching the fuel cell between a normal operating mode, in that a relatively high flow rate is supplied to fuel of the anode and to the oxidizing agent of the cathode, and a return mode includes, in which a relatively low flow rate of fuel together with oxidant supplied in the recycle fluid, is fed into the fuel supply line. The method of claim 19, further comprising the step controlling the flow rate of the fuel and / or the oxidizing agent to a predetermined Measure To achieve humidification of the fuel flow, which is supplied to the anode. The method of claim 19, further comprising the step controlling the flow rate of the fuel and / or the oxidizing agent to a predetermined Measure preheating reach the fuel flow, which is supplied to the anode.